As Hodgman pointed out, "stack" doesn't imply a particular implementation: It just means it's a data structure where you push things ("stack frames", in this case) at the top and you only ever access the top thing. Whether this is implemented by moving a pointer in an array or by using a sliding window of an array of registers (Sparc) or by a linked list, it's still a stack.

As to the phrase 'on the heap' when referring to the free store, there was never a heap in the technical computer-science sense of the word.